Semiconductor device, display device, and electronic apparatus

ABSTRACT

To prevent an electrostatic damage on a display device formed with a driving circuit. Protective circuits are provided not only at input terminal parts, but also at intermediate parts of a circuit or at the ends of wiring lines. Otherwise, the protective circuits are provided at the ends of the wiring lines and at the places immediately before and after the input terminals, respectively, and then the circuit is interposed therebetween. Further, the protective circuits are provided around a circuit with a large current consumption.

BACKGROUND

The present invention relates to a semiconductor device, display device and electronic apparatus, and more particularly, to a display device having a driving circuit provided on an active matrix substrate.

In a semiconductor device, it is important to take measure against the electro-static damages (ESD) when a high voltage caused by a static electricity or a various noise phenomenon is unintentionally applied to the inside of the device to damage an insulating film, thereby causing a fatal damage to the device. In order to prevent the problem, various protective circuits have been proposed. For example, in Patent Documents 1 and 2, it has been proposed that an abnormal voltage applied to lines is discharged to GND, etc. by proper combination of diodes. However, since general semiconductor devices are formed on a silicon wafer made of conductive material, there are little chances of being electrified within the semiconductor device, so that it is a key issue to prevent the damage when a static electricity flows through input terminals. To solve such a problem, conventionally, protective circuits are formed between input terminals and the semiconductor device forming a circuit, i.e., immediately after the input terminals, so that it is prevented that the high voltage from the input terminals is transmitted to the device.

On the other hand, in a display device using an active element such as a thin film transistor (TFT), which has been rapidly spread in recent years, a device is formed on an insulating substrate. As a result, there is a problem in that it is easy that the device is easily electrified by static electricity, and that the electro-static damage is generated during the manufacturing process. On this account, for example, an electro-static measure is taken by forming an antistatic line, called as a guide ring or a short ring, at the periphery of an active matrix circuit.

In recent years, a display device having a built-in driving circuit has been widely spread, in which an improvement of a definition, a cost reduction and better reliability are realized by using a polysilicon TFT having polysilicon serving as an active layer. In such a device, as a measure against the static electricity of the driving circuit, a conventional method used in a semiconductor on a silicon wafer is applied as it is, so that only protective circuits for preventing the static electricity from the input terminals are built in, and a conventional method of a display device not having the built-in driving circuit is used to protect the active matrix circuit from the static electricity. Hereinafter, the conventional art relating to the protection of the driving circuit will be described in detail with respect to FIG. 11.

FIG. 11 is a view illustrating a configuration of an active matrix substrate of a VGA-LCD using polysilicon TFT by the conventional art. Reference numerals 201-1 to 201-480 indicate scanning lines of the active matrix circuit, driven by a scanning line driving circuit 800. Reference numerals 202-1 to 202-1920 indicate data lines, and pixel transistors 401 composed of n-type transistors and pixel electrodes 402 are formed at intersections of the scanning lines and the data lines, respectively, to drive a liquid crystal device.

Reference numerals 801-1 to 801-480 indicate scanning line driving unit circuits composed of 480 stages, which form the scanning line driving circuit 800, and each of them is composed by a CMOS circuit. A specific configuration of the scanning line driving unit circuits 801-1 to 801-n is shown in FIG. 5.

Each of the scanning line driving unit circuits 801-1 to 801-480 is connected to a low potential power line 750 and a high potential power line 751, through which power is supplied. The low potential power line 750 is connected to a low potential power terminal 650, the high potential power line 751 is connected to a high potential power terminal 651. Also, the low potential power terminal 650 and the high potential power terminal 651 are connected to a power IC through a FPC, and they are supplied with reference potentials of a potential VS and a potential VD, respectively. Herein, VS is less than VD.

Further, a signal (for example, a clock signal) required for the operation of each of the scanning line driving unit circuits 801-1 to 801-480 are supplied from an external IC through signal lines 701 and 702 and signal terminals 601 and 602.

Here, in order to prevent TFTs constituting each of the scanning line driving unit circuits 801-1 to 801-480 from being damaged by the static electricity or noise current input through the low potential power terminal 650, the high potential power terminal 651 and the signal terminals 601 and 602, static electricity protection circuits ESD1 to ESD4 are provided between the input terminals 601, 650 and 651 and the scanning line driving unit circuits 801-1 to 801-480, respectively. A specific configuration of the static electricity protection circuit ESD1 to ESD4 is shown in Patent Document 1 and Patent Document 2.

[Patent Document 1] Japanese Patent No. 2884946

[Patent Document 2] Japanese Patent No. 3141511

However, in the driving circuit on an insulating substrate, it is difficult for charges to escape as compared to the circuit on silicon wafer, and it is easy to be electrified. In addition, in the case that the driving circuit of the display device is formed on a glass substrate, the area of the circuit is larger as compared to the IC formed on a general silicon wafer. Therefore, in such a configuration, there is a problem in that a protection of the wiring lines far from the input terminals against the static electricity is not sufficient, especially during a manufacturing process. Specifically, since there is a possibility that the static electricity is electrified on a certain location on the substrate during the manufacturing process, when the distance from the electrified location to the static electricity protection circuit is long and the line resistance is high, a transistor within a circuit located closer than the static electricity protection circuit is damaged by the static electricity even before the static electricity protection circuit starts the operation. Such a problem is the same in a semiconductor device using a SOI substrate.

Further, in a case of an insulating substrate, a large current may flow in the wiring lines by electrostatic induction when strong electrostatic discharge occurs in the outside of the substrate even in a finished product state after completion of the manufacturing process. Even in such a case, there is a possibility that a circuit located far from the terminal is damaged.

Furthermore, the present invention provides a measure against the problem in that potentials on the wiring lines are instantaneously changed, when a large amount of current flows in the wiring lines through a circuit.

SUMMARY

In order to solve the above problems, it is proposed that a semiconductor circuit be disposed between protective circuits and input terminals. More specifically, it is proposed that an electrical resistance between a connection part connecting the semiconductor circuit to wiring lines and input terminals be lower than an electrical resistance between a connection part connecting the protective circuits to the wiring lines and the input terminals.

Thus, there is an effect that the protection against the static electricity is sufficiently obtained even in a place far from the terminal, by providing internal protective circuits in an area which is not connected to the input terminals of the wiring lines as well as providing the protective circuits around the input terminals as in the conventional art.

Further, it is proposed that a plurality of the protective circuits are arranged on the wiring lines and the semiconductor circuit is interposed between the protective circuits. Thereby, it is possible to prevent the static electricity or noise input from the input terminals, and to protect a semiconductor circuit far from the input terminals. In addition, it is preferable that the plurality of the protective circuits be arranged with a predetermined gap therebetween, thereby the entire part of the semiconductor circuit connected to the wiring lines can be protected.

Furthermore, in the present invention, it is proposed that the wiring line include a low potential power line and a high potential power line, and the protective circuits between power sources connected to both of the low potential power line and the high potential power line is comprised. In this configuration, the protective circuit can be easily formed by a diode element, etc., and since all are power lines, it is difficult to be affected by the noise. Also, in general, the power line is remarkably lengthened within a circuit, so that it requires a static protection more than other lines. Therefore, the effect is remarkable. In addition to this, for a signal line, it is proposed that the protective circuits between signal power sources be formed between the power lines. Since it is easy to be affected by the noise between the signal lines, it is possible to reduce an adverse influence by providing the protective circuit between the power source and the signal line. Also, it is proposed that the capacitance of the protective circuits between signal power sources be lower than the capacitance of the protective circuits between the power sources. In this way, it is possible to minimize an influence on the power line by the signal.

Further, in the present invention, the capacitive component between the wiring lines in the protective circuits is not less than I×t×0.1 (F) when the maximum current flowing in the low potential power line or the high potential power line is I (A) and the maximum tolerable time when a voltage drop in power line occurs is t (second). t is preferably below 10⁻⁸ (second) in consideration of general operation time in a polysilicon TFT. Thereby, when a large amount of current flows in the circuit and a supply from the outside is not sufficient to follow it to generate instantaneous voltage changes on the wiring lines, there is an effect that the voltage changes are reduced by the capacitive components within the protective circuits.

Further, in the present invention, it is proposed that the protective circuit between power sources or the protective circuit between signal power sources include a diode element, and one end of the diode element is connected to the power line. In this configuration, the static electricity or the noise current is easily discharged, so that the protective performance is remarkably improved.

Further, in the present invention, it is proposed that contents of the invention described above is applied to a so-called CMOS type semiconductor device, which is composed of an n-channel type field effect transistor and a p-channel type field effect transistor. Because the CMOS type semiconductor device requires at least 2 types of reference power source, the number of power line is increased, so that the effect of this invention is remarkable. Particularly, in the CMOS type semiconductor device composed of the polysilicon thin film transistor, the substrate is an insulating substrate, and thus electrification easily occurs under a state in which there is no protective circuit, so that the effect of the present invention is more prominent. Further, when an active matrix used in a TFT-LCD or TFT-OLED and a driving circuit thereof are formed on the insulating substrate, the driving circuit is configured to surround the active matrix, so that it becomes larger and accordingly its line is also lengthened. As a result, the effect of the present invention is more remarkable.

Further, in the present invention, it is proposed that, when the active matrix is applied to the present invention, internal protective circuits are arranged at corners far from the input terminals among four corners of the active matrix. By such a configuration, it is possible to arrange large-sized protective circuits without making the peripheral area large.

Moreover, in a display device using the semiconductor device of the present invention and an electronic apparatus having the display device, the electro-static damage is difficult to be generated during a manufacturing process, so that it is advantageous in terms of cost, and it is difficult that the voltage drop at the power source occurs, so that there is an effect that the display quality is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a configuration of an active matrix substrate for explaining a first embodiment of the present invention;

FIG. 2 is a view illustrating a scanning line driving circuit for explaining a second embodiment of the present invention;

FIG. 3 is a view illustrating a configuration of an active matrix substrate for explaining a third embodiment of the present invention;

FIG. 4 is a view illustrating a protective circuit for explaining embodiments of the present invention;

FIG. 5 is a view illustrating a scanning line driving unit circuit for explaining embodiments of the present invention;

FIG. 6 is a perspective view (partially sectional view) of a liquid crystal display device for explaining the first embodiment of the present invention;

FIG. 7 is a view illustrating a buffer circuit for explaining the third embodiment of the present invention;

FIG. 8 is a view illustrating a buffer circuit for explaining another example of the third embodiment of the present invention;

FIG. 9 is a view illustrating a protective circuit for explaining the third embodiment of the present invention;

FIG. 10 is a graph illustrating a simulation result of a reference potential change for explaining the third embodiment of the present invention; and

FIG. 11 is a view illustrating a configuration of an active matrix substrate for explaining the conventional example.

DETAILED DESCRIPTION OF EMBODIMENTS

Even in a case of forming a complementary circuit other than the buffer circuit described in the present embodiment, such as a data line driving circuit, DAC circuit, power circuit, level shift circuit, memory circuit, etc. on the active matrix substrate, it is preferable to provide the protective circuits at the end or intermediate of a branched power line, and it is more preferable that all circuits are located on the power line between protective circuits. Also, it is preferable in terms of reduction of the power noise that protective circuits having a capacitance not less than a predetermined value are provided at the front and rear ends of the circuit having high current consumption. Specifically, when the current consumption of the circuit is I and the tolerable time when the voltage drop occurs (typically, t≦10⁻⁸ (second)), it is preferable to have the capacitance not less than I×t×0.1 (F)).

With respect to the configuration of the active matrix substrate and the details of the protective circuits or the driving circuit in a place other than the above specified place, the third embodiment is the same as the first embodiment. Also, for the liquid crystal display device using the active matrix substrate shown in FIG. 3, the configuration is the same as in the first embodiment, so that the explanation is omitted.

Further, in the first embodiment, only the protective circuit of FIG. 4 has been described, however, it is possible to obtain the same effect as in the third embodiment by providing the protective circuit of FIG. 9.

INDUSTRIAL APPLICABILITY

The present invention is not limited to the above-mentioned embodiments, but it can be also applicable to a liquid crystal display using an active matrix substrate formed with a data line driving circuit, a DAC, a power circuit, etc. In this case, the present invention may be applicable to each of the circuits, or it may be applied to some of the circuits if there is any problem in layout, and so on. In case of applying it to the scanning line driving circuit, various sequential selection circuits as well as the shift register circuit as in the embodiment are possible.

Further, the protective circuits can have the same configuration as in the embodiment and foregoing examples, and any configurations which have been suggested so far can be used.

Further, instead of a polysilicon transistor, an amorphous silicon thin film transistor may be used. Also, instead of a thin film transistor formed on the insulating substrate, an active matrix substrate may be used, in which a pixel switching element or a driving circuit is formed on a crystal silicon wafer.

Further, as a liquid crystal display device, it may be a reflective type or a transflective type instead of the transmission type, and it may be a projection type light value instead of a direct viewing type light value. Also, a normally black mode can be used instead of a normally white mode as in the embodiment. Especially, in this case, a vertical alignment mode or a horizontal electric field switching mode may be possible as an alignment mode of the liquid crystal. 

1. A semiconductor device comprising: a plurality of semiconductor circuits arranged on a substrate; wiring lines electrically connected to the semiconductor circuits; input terminals electrically connected to the wiring lines to supply electrical signals; and protective circuits connected to the wiring lines to protect the wiring lines or the semiconductor circuits from static electricity or noise, wherein at least one semiconductor circuit among the semiconductor circuits is disposed between the input terminals and the protective circuits.
 2. The semiconductor device according to claim 1, wherein the electrical resistance between a connection part connecting the at least one semiconductor circuit among the plurality of semiconductor circuits to the wiring lines and a connection part connecting the wiring lines to the input terminals, is lower than the electrical resistance between a connection part connecting the protective circuits to the wiring lines and a connection part connecting the wiring lines to the input terminals.
 3. The semiconductor device according to claim 1, wherein a plurality of the protective circuits are arranged, and at least one semiconductor circuit among the semiconductor circuits is arranged between the protective circuits.
 4. The semiconductor device according to claim 3, wherein the plurality of protective circuits are arranged with a predetermined gap therebetween.
 5. The semiconductor device according to claim 1, wherein the wiring lines include a low potential power line that supplies at least relatively low reference potential and a high potential power line that supplies relatively high reference potential, and at least one protective circuit is connected to both of the low potential power line and the high potential power line to form a power source protective circuit.
 6. The semiconductor device according to claim 5, wherein the input line has a signal input line that transmits a signal which is not a fixed reference potential, and at least one protective circuit is a protective circuit between signal power sources, in which either the low potential power line or the high potential power line is connected to the signal line.
 7. The semiconductor device according to claim 5, wherein a capacitive element is provided at least between the low potential power line and the high potential power line, or between the signal line and the low potential power line, or between the signal line and the high potential power line, and the capacitance of the capacitive element is not less than I×t×0.1 (F) when the maximum current flowing in the low potential power line or the high potential power line is I (A), and smaller one of tolerable times when a voltage drop in the low potential power line or in the high potential power line occurs is t (second).
 8. The semiconductor device according to claim 7, wherein t is not more than 10⁻⁸ (second).
 9. The semiconductor device according to claim 6, wherein the capacitance between the signal input line and the low potential power line or the high potential power line is lower than the capacitance between the low potential power line and the high potential power line.
 10. The semiconductor device according to claim 1, wherein at least one of the power source protective circuit and the signal power source protective circuit includes a diode element, and one end of the diode element is connected to either the low potential power line or the high potential power line.
 11. The semiconductor device according to claim 5, wherein each of the plurality of semiconductor circuits includes a first transistor being an n-channel type field effect transistor and a second transistor being a p-channel type field effect transistor, and at least a part of the first transistor is connected to the low potential power line and at least a part of the second transistor is connected to the high potential power line.
 12. The semiconductor device according to claim 11, wherein each of the first transistor and the second transistor has a polysilicon thin film serving as an active layer, and the substrate is an insulating substrate.
 13. The semiconductor device according to claim 1, wherein a plurality of active elements are formed in a matrix on the substrate, and at least a part of the plurality of semiconductor circuits constitutes a driving circuit for supplying a drive signal to the plurality of active elements.
 14. The semiconductor device according to claim 13, wherein internal protective circuits are arranged at corners far from the input terminals among four corners of the plurality of active elements arranged in the matrix shape.
 15. A display device including: a first substrate having the semiconductor device according to claim 1 formed thereon, a second substrate opposing the first substrate, and a liquid crystal layer interposed between the first substrate and the second substrate.
 16. A display device including the semiconductor device according to claim 1, on which an organic EL element is formed.
 17. An electronic apparatus having the display device according to claim
 15. 